Signatures of Chaos: A study in predictability of flows

This work explores predictability in atmospheric flows. A study on forecasting is conducted in the Lorenz [1963] model using several Data Assimilation techniques. Methods of statistically combining model forecasts with observations for prediction are tested for their performance, which readily extend to higher dimensional systems and are oft encountered in Numerical Weather Prediction. Next, predictability in resolved three dimensional turbulence is investigated using high resolution flow simulations that provide an exciting avenue for forecasting or coupling with large scale circulation models. The Dutch Atmospheric Large Eddy Simulation (DALES) is adapted to study the evolution of perturbations in LES and DNS of a dry convective boundary layer. The effects of parameters like the perturbation magnitude, its wavenumber and location, and the flow Reynolds number are studied to find the governing modes of error growth. The implications on predictability in a system with a superposition of multiple scales are then discussed.Solid and Fluid MechanicsMechanical EngineeringMechanical, Maritime and Materials Engineerin

Unravelling Turbulent Emulsions with lattice-Boltzmann simulations

The mixing of two immiscible fluids, often under turbulent conditions, can lead to the formation of an emulsion, where droplets of one fluid are embedded in another fluid. The occurrence of emulsions is commonplace across industries, ranging from the oil industry to food processing and biotechnology. Why emulsions serve diverse applications, in grossly simple terms, is due to their structural organization, as the two fluids in an emulsion form exhibit very different physical properties than they do when separated. The stability of the emulsion structure, hence, is key for its utility. The presence of impurities, or surfactants, in the constituent fluids, greatly enhances emulsion stability, by preventing the coalescence of droplets (which would lead to phase segregation). Emulsion research, over the past century, has developed into a thriving field, driven by the force of detailed experimentation that has significantly informed modeling, control and design of processes dealing with emulsification.Despite being predictable to a degree, the true nature of droplet dynamics at theheart of emulsification remains unknown. It is experimentally exceedingly difficult to illumine the evolution of interfaces undergoing coalescence and breakup, while simultaneously reporting the three-dimensional, turbulent flow features. It is slowly becoming feasible, however, to tackle these problems by using numerical simulations. Such simulations, too, involve a level of modeling complexity and pose heavy computational demands, and have hence remained an exception. It is only now becoming feasible to simulate such complex flows, allowing us to augment experiments with numerical insights. In this thesis, we attempt to unravel emulsification (to a small extent) by using simulations resolving both flow and interfaces, while considering fluids with impurities.OLD SnC CultureChemE/Transport Phenomen

Correlation and decomposition concepts for identifying and disentangling flow structures: Framework and insights into turbulence organization

Turbulence and its organization, long conceptualized in terms of "coherent structures,"has resisted clear description. A significant limitation has been the lack of tools to identify instantaneous, spatially finite structures, while unraveling their superposition. We present a framework of generalized correlations, which can be used to readily define a variety of correlation measures, aimed at identifying field patterns. Coupled with Helmholtz-decomposition, this provides a paradigm to identify and disentangle structures. We demonstrate the correlations using vortex-based canonical flows and then apply them to incompressible, homogeneous, isotropic turbulence. We find that high turbulence kinetic energy (Ek) regions form compact velocity-jets that are spatially exclusive from high enstrophy (ω 2) regions that form vorticity-jets surrounded by swirling velocity. The correlation fields reveal that the energetic structures in turbulence, being invariably jets, are distinct from those in vortex-based canonical flows, where they can be jet-like as well as swirling. A full Biot-Savart decomposition of the velocity field shows that the velocity-jets are neither self-induced, nor induced by the interaction of swirling, strong vorticity regions, and are almost entirely induced, non-locally, by the permeating intermediate range (rms level) vorticity. Velocity-swirls, instead, are a superposition of self-induced and background-induced velocity. Interestingly, it is the mild intermediate vorticity that dominantly induces the velocity-field everywhere. This suggests that turbulence organization could result from non-local and non-linear field interactions, leading to an emergent description unlike the notion of a strict structural hierarchy. Our correlation-decomposition framework lends itself readily to the study of generic vector and scalar fields associated with diverse phenomena.Accepted Author ManuscriptChemE/Transport Phenomen

Simulating liquid droplets: A quantitative assessment of lattice Boltzmann and Volume of Fluid methods

While various multiphase flow simulation techniques have found acceptance as predictive tools for processes involving immiscible fluids, none of them can be considered universally applicable. Focusing on accurate simulation of liquid-liquid emulsions at the scale of droplets, we present a comparative assessment of the single-component multiphase pseudopotential lattice Boltzmann method (PP-LB, classical and modified) and the Volume of Fluid method (VOF, classical and modified), highlighting particular strengths and weaknesses of these techniques. We show that a modified LB model produces spurious velocities 1–3 orders of magnitude lower than all VOF models tested, and find that LB is roughly 10 times faster in computation time, while VOF is more versatile. Simulating falling liquid droplets, a realistic problem, we find that despite identical setups, results can vary with the technique in certain flow regimes. At lower Reynolds numbers, all methods agree reasonably well with experimental values. At higher Reynolds numbers, all methods underpredict the droplet Reynolds number, while being in good agreement with each other. Particular issues regarding LB simulations at low density ratio are emphasized. Finally, we conclude with the applicability of VOF vis-à-vis PP-LB for a general range of multiphase flow problems relevant to myriad applications.Accepted Author ManuscriptChemE/Transport PhenomenaIntensified Reaction and Separation System

Editorial: Solutions to water crises (related to actual interventions)

Water Resource

A 3 ppm 1.5 × 0.8 mm2 1.0 µA 32.768 kHz MEMS-based oscillator

ThisAccepted Author ManuscriptElectronic Instrumentatio

Never Ask for a Lighter Rain but a Stronger Umbrella

In a recent editorial in the journal Nature Sustainability, the editors raised the concern that journal submissions on water studies appear too similar. The gist of the editorial: “too many publications and not enough ideas.” In this response, we contest this notion, and point to the numerous new ideas that result from taking a broader view of the water science field. Drawing inspiration from a recently hosted conference geared at transcending traditional disciplinary silos and forging new paradigms for water research, we are, in fact, enthusiastic and optimistic about the ways scientists are investigating political, economic, historical, and cultural intersections toward more just and sustainable human-water relations and ways of knowing.Water Resource

Individual participants

Any software made available via TimeCenter is provided \as is " and without any express or implied warranties, including, without limitation, the implied warranty of merchantability and tness for a particular purpose. The TimeCenter icon on the cover combines two \arrows. " These \arrows " are letters in the so-called Rune alphabet used one millennium ago by the Vikings, as well as by their precedessors and successors, The Rune alphabet (second phase) has 16 letters. They all have angular shapes and lack horizontal lines because the primary storage medium was wood. However, runes may also be found on jewelry, tools, and weapons. Runes were perceived by many ashaving magic, hidden powers. The two Rune arrows in the icon denote \T " and \C, " respectively. Real-Time Database Systems (RTDBSs), have attracted considerable amount of research attention in the recent past and a number of important applications have been identi ed for such systems, such as telecommunications network management, automated air tra c control, automated nancial trading, process control and military command and control systems. Due to th